Adjustable voltage transformer



Patented Jan. 2 2, 1952 ADJUSTABLE VOLTAGE TRANSFORMER Charles E. Nobles, Baltimore, and Reuben Lee,

Linthicum Heights, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 4, 1947, Serial No. 784,034 2 Claims. (Cl. 171-119) This invention relates to electrical transformers and particularly to adjustable voltage transformers for supplying an alternating voltage that is adjustable to a desired value.

In certain industrial applications, it is necessary to maintain aconstant voltage supply to a piece of electrical apparatus. For example, the plate voltage of an electronic tube used in certain applications in radio systems requires a constant voltage supply.

In order to provide such a constant voltage supply, it has been the usual practice to provide a plate transformer for supplying current to the plate circuit and a variable voltage auto-transformer arranged for supplying voltage to the primary winding of the plate transformer. The auto-transformer in such a system is so arranged that the voltage supplied from the auto-transformer to the plate transformer may be adjusted by varying a tap connection to maintain the desired constant plate voltage.

It is an object of our invention to provide a single transformer unit that is capable of combining the-functions of both the auto-transformer and the plate transformer described above, and that is economical to manufacture and readily adjustable to provide a desired voltage output.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention, reference being had to the accompanying drawing, in which:

Figure 1 is a diagrammatic view of a prior art apparatus and circuits therefor, employing two transformer units;

Fig. 2 is a diagrammatic view of the apparatus and circuits comprising the invention;

Fig. 3 is an end elevational view of a core and coil structure of a transformer embodying the invention; and

Fig. 4 is a side elevational view of the structure shown in Fig. 3.

Referring to the drawing, the diagram in Fig. I illustrates a conventional arrangement of a variable voltage auto-transformer I having a winding 2 that is supplied with alternating voltage from a source of electrical energy, indicated by the conductors 3 and 4, for delivering an output voltage through conductors 5 and 6. The output voltage from the auto-transformer l is supplied to a primary winding 1 of a constant ratio transformer 8 from the secondary winding Hioi' which conductors l2 and 13 extend for supplying voltage to a load. An adjustable tap connection I4 is provided which may be so adjusted as to impress a voltage across the conductors I, and 6 having any desired relation to the voltage impressed across the auto-transformer winding 2 from the conductors 3 and 4.

Fig. 2 is a diagrammatic view of a variable voltage transformer organized in accordance with the invention. The transformer unit 2| comprises a magnetic core loop 22 forming a closed magnetic circuit path having an upper Winding leg 23 and a lower winding leg 24. Primary circuit conductors 25 and 23 represent a source of alternating current energy for impressing a voltage upon the primary winding of the transformer, which consists of a winding portion 21 wound about the winding leg 23 of the core structure and a winding portion 28 wound about the lower winding leg 24 of the core structure, the two primary winding portions 21 and 28 being shown connected in series circuit relation between the primary circuit conductors 25 and 26. It is possible, in some cases, to use these two winding portions 21 and 28 connected in parallel circuit relation to each other. This gives a wider range of voltage ratio than the series connection, although the volts per turn are higher when the sliding contact member is near the extreme ends of the winding.

A sliding contact member 29 is shown connected to the primary circuit conductor 26 and arranged for making contact with a selected turn of the primary winding portion 28 to vary the number of turns connected in circuit between the primary circuit conductors 25 and 26, to thereby adjust the output voltage from the transformers. A secondary winding 3| is provided about the wind ing leg of the core 23 and the primary winding portion 2'. associated with the upper core leg for supplying voltage to the secondary circuit conductors 32 and 33. As the contact member 29 is moved from engagement with one turn of the winding portion 28 to another turn thereof, the total number of primary winding turns included in circuit between the primary circuit conductors 25 and 26 is varied, thus varying the voltage per turn impressed upon the primary winding and consequently the magnetic flux induced in the core 22. Thus, the voltage per turn induced in the secondary winding 31 is varied, which, in turn, varies the output voltage of the transformer delivered across secondary circuit conductors 32 and 33. Thus, by movement of the contact member 29, the ratio between the input voltage impressed across the primary circuit conductors 25 and 26 and the output voltage delivered across the secondary circuit conductors 32 and 33, may be adjusted to any desired value within the range of the transformer unit.

Referring to Figs. 3 and 4, the magnetic core loop 22 may be of the wound-core type of construction in which a ribbon of magnetic sheet steel is wound layer upon layer and held together by a steel strap 34 in a well known manner. The primary winding portion 21, best shown in Fig. 3, is wound about a tube of insulating material 35 extending about the upper winding leg of the core structure and beyond the straight portion of the winding leg, as shown at 35 in Fig. 4. The primary winding portion 28 may be wound about a tube of insulating material 36 that is positioned about the lower winding leg portion 24 of the core structure, and extends beyond the straight portion of the winding leg at both ends, as best shown in Fig. 4:. Winding terminals 4! and 32 for the primary winding portion 2'! are shown in Fig. 4, mounted on the opposite ends of the insulating tube 35, and winding terminals 43 and id for the primary winding portion 23 are shown mounted on the opposite ends of the insulating tube 3%. The secondary winding 3i may be wound about a tube of insulating material d5, as best shown in Fig. 3, and positioned about the upper leg of the transformer core containing the winding portion 2'? which is the untapped portion.

The entire structure is supported upon a frame including a U-shaped frame member 54 provided at the upper ends thereof with bolts 52 for supporting a member 53 extending through the openings in the windings to support the winding structure from the two upper ends of U-shaped member 5i. The core member 22 may be supported, in part, from the coil structure and, in part,'from the frame members 55 attached to the two opposite vertical portions of the U-shaped frame member 56. Bracket members 5E5 are also shown attached to the vertical frame members 5H for assisting in supporting the core member 22.

The contact member 29, as best shown in Fig. 3, is supported at the upper end of a slidable arm El spaced from the frame 5i by a collar 58 through which extends a shaft 53 that is attached to the collar 6! on the opposite side of the frame by means 01 pins 52 extending through the shaft 59. A spring "53 is provided for biasing the shaft 58 and the arm 5? attached thereto toward the left, as viewed in Fig. 3. A spring 64 is provided for engaging the head 65 at the upper end of the arm 57 so as to bias it and the contact member 29 toward the left, as viewed in Fig. 3, or into tight engagement with the turns of the primary winding portion 28. A conductor 56 is provided for connecting the contact member 29 through the head 65 to the terminal 67 which may, in turn, be connected to the primary circuit conductor 2%. The arm 51, carrying the contact member 29, is slidable to the right and to the left, as viewed in Fig. l, between the limits indicated by the stops 6B and 59. It will be noted that the convolutions or the primary winding portion 28, as shown in Figs. 3 and are bare conductors so that any turn thereof is adapted to engage the contact member 29 when this contact member is moved to the desired position for engaging any particular turn of the winding portion.

It will be noted that the tapped portion 28 of the primary winding, by being placed on the other of the two winding legs of the core from the winding portion 27, is readily exposed to be easily engaged by the contact member '29 and that the mechanism for operating the contact 2:? is free from complications which would result if it were attempted to position the secondary winding 3i about the turns of the entire primary winding. Thus, a portion of the primary winding 21 is positioned within the turns of the secondary winding 3i and all of these primary winding turns remain continuously in the primary winding circuit, and a second portion of the primary winding 28 is positioned about another leg of the core structure about which the secondary windings are not positioned, thus leaving these winding turns readily accessible to the tap-changing mechanism for carrying 4 the contact member 29 'to engage a desired turn of the winding portion '28.

All of the primary winding turns might be on the winding leg 24, and all the secondary turns on the winding leg 23. However, this gives poor coupling between the two windings, and the arrangement illustrated and .described having part of theprimary turns on the core leg 23 and closely coupled to the secondary winding gives much better coupling between the primary and secondary windings.

It will be apparent to one skilled in the art that modifications may be made in the details of the structure and circuits illustrated and described within the spirit of the invention, and we .do not wish to be limited otherwise than in accordance with the scope of the appended claims.

We claim as our invention:

1. In an electrical transformer, a magnetic core structure comprising aclosed magnetic.circuit path having two parallel winding legs, a primary winding comprising two winding portions connected in series circuit relation, one of the two primary winding portions being positioned about one of-the twowin'ding legs of the core and the other ofthe-two primary winding portions being positioned about the other of the two winding legs of the core,-a secondary winding positioned about one oi-the primary winding portions on one winding leg of the core, a slidable contact arm carrying a contact member at one end thereof for engaging a selected one of the conductor turns of the other of the two primary winding portions, said arm and contact member being adjustable for connecting a circuit conductor to a selected turn of the primary winding portion for adjusting the'ratio between the input voltage and the output voltage of the transformer.

2. In an electrical transformer, a magnetic core structure comprising a closed magnetic circuit path having two parallel winding legs,'a primary winding comprising two winding portions connected in series circuit relation, one of the two primary winding portionsbeing positioned about one of the two winding legs of the core and the other of the two primary winding-portions being positioned about the other of the two winding legs of the core, a secondary winding positioned about one of the primary winding portions on one winding leg of the core, primary circuit conductors for connecting the primary winding to a source of electrical energy and secondary circuit conductors for connecting the secondary winding to a load, a slidable contact arm and a contact member carried thereby for connecting a primary circuit conductor to a selected turn of the second-named primary winding portion for adjusting the ratio between the transformer input voltage and the transformeroutput voltage.

CHARLES E. NOBLES. REUBEN LEE.

REFERENCES CITED The following references'are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,036,445 Burnham ..'.Aug. 20, 1912 1,397,298 Seede Nov. 15, 1921 1,5l9 062 Shroder a- Dec/9, 1924 1,873,975 Meyerhans Aug. 30, 1932 2,408,017 Garretson Sept. 24,1946 

